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Muscle funccellularlevel animal systems
1. MO Figure
Muscle Function at
the Cellular Level
Michael Patrick O'Neill/Science Source.
2. Functions of Muscular Tissue
• Like nervous tissue, muscles are excitable
or "irritable”
they have the ability to respond to a stimulus
• Unlike nerves, however, muscles are also:
Contractible (they can shorten
in length)
Extensible (they can extend or
stretch)
Elastic (they can return to their
original shape)
3. Functions of Muscular Tissue
• Muscle makes up a large percentage of the
body’s weight
• Their main functions are to:
Create motion – muscles work with nerves,
bones, and joints to produce body movements
Stabilize body positions and maintain posture
Store substances within the body using
sphincters
4. Three Types of Muscular
Location Function Appearance Control
Skeletal
skeleton
movement,
heat, posture
striated, multi-nucleated
(eccentric),
fibers parallel
voluntary
Cardiac
heart
pump blood
continuously
striated, one central
nucleus
involuntary
Visceral
(smooth muscle)
G.I. tract,
uterus, eye,
blood vessels
Peristalsis,
blood pressure,
pupil size,
erects hairs
no striations, one
central nucleus
involuntary
Tissue
5. Three Types of Muscular Tissue
(a) Skeletal muscle
(b) Cardiac muscle (c) Visceral smooth muscle
6. Location Function Appearance Control
Skeletal
skeleton
movement,
heat, posture
striated, multi-nucleated
(eccentric),
fibers parallel
voluntary
Cardiac
heart
pump blood
continuously
striated, one central
nucleus
involuntary
Visceral
(smooth muscle)
G.I. tract,
uterus, eye,
blood vessels
Peristalsis,
blood pressure,
pupil size,
erects hairs
no striations, one
central nucleus
involuntary
Skeletal Muscle
8. Skeletal Muscle
Skeletal muscle fibers are very long “cells” - next to
neurons (which can be over a meter long),
perhaps the longest in the body
The Sartorious muscle contains
single fibers that are at least
30 cm long
A single skeletal muscle fiber
9. Motor neuron
Sarcolemma
Skeletal Muscle
The terminal processes of a motor
neuron in close proximity to the
sarcolemma of a skeletal muscle fiber
10. Skeletal muscle fibers
A muscle fiber consists of a single cell.
• The cell is long and multinucleated.
• The cytoplasm is called the sarcoplasm.
• Contains a specialized ER, called the
sarcoplasmic reticulum, that stores
calcium.
• Contains myofibrils made up of thick and
thin filaments.
11. The Skeletal Muscle Fiber
Increasing the level of magnification, the myofibrils are
seen to be composed
of filaments
Thick filaments
Thing filaments
12. The Skeletal Muscle Fiber
• The basic functional unit of skeletal muscle
fibers is the sarcomere: An arrangement of
thick and thin filaments sandwiched between
two Z discs
A scanning electron micrograph of a sarcomere
13. The Skeletal Muscle Fiber
• Muscle contraction occurs in the sarcomeres
The “Z line” is really a Z disc when considered in 3
dimensions. A sarcomere extends from Z disc to Z disc.
14. Muscle Proteins
• Myofibrils are built from three groups of
proteins
Contractile proteins generate force during
contraction
Regulatory proteins help switch the contraction
process on and off
Structural proteins keep the thick and thin
filaments in proper alignment and link the
15. Muscle Proteins
• The thin filaments are comprised mostly of
the structural protein actin, and the thick
filaments are comprised mostly of the
structural protein myosin
16. Muscle Proteins
• In the thin filaments actin proteins are strung
together like a bead of pearls
• In the thick filaments myosin proteins look
like golf clubs bound together
17. Muscle Proteins
In this first graphic, the myosin binding sites on the actin
proteins are readily visible.
The regulatory proteins troponin and tropomyosin have
been added to the bottom graphic: The myosin binding
sites have been
covered
18. Muscle Proteins
In this graphic the troponin-tropomyosin complex has
slid down into the “gutters” of the actin molecule
unblocking the myosin binding site
Myosin binding site exposed
The troponin-tropomyosin complex can slide back and
forth depending on the presence of Ca2+
19. Muscle Proteins
• Ca2+ binds to troponin which changes the shape of
the troponin-tropomyosin complex and uncovers
the myosin binding sites on actin
20. Muscle Proteins
• Besides contractile and regulatory proteins, muscle
contains about a dozen structural proteins which
contribute to the alignment, stability, elasticity, and
extensibility of myofibrils
• Titan is the third most plentiful protein in muscle,
after actin and myosin - it extends from the Z disc and
accounts for much of the elasticity of myofibrils
• Dystrophin is discussed later as it relates to the disease
of muscular dystrophy
21. The Sliding-Filament
Mechanism
• With exposure of the myosin binding sites on
actin (the thin filaments)—in the presence of
Ca2+ and ATP—the thick and thin filaments
“slide” on one another and the sarcomere is
shortened
23. Figure 1
Sliding filament model
Thick (myosin) and thin (actin) filaments slide past one another
during muscle contraction. As a result, the sarcomere shortens.
24. Figure 2
Sarcomeres
C. F. Armstrong/Science Source.
Z-discs form dark lines in electron micrographs and give
skeletal muscle a striated appearance.
29. Muscle energy storage
Glycogen
• Glucose polymer. Glucose is used in
cellular respiration to make ATP.
Creatine phosphate
• Transfers a phosphate to ADP to form
ATP.
30. Figure 5
Muscle innervation
Muscle fibers can be innervated by a single neuron, which
increases contraction strength at the expense of fine control, or by
multiple neurons, which allows finer control but with little strength.
34. Figure 7
Regulation of contraction
In resting muscle,
tropomyosin covers
myosin-binding sites
on actin. The
troponin complex
holds tropomyosin in
place. Ca2+ binding
to troponin causes
tropomyosin to shift,
which exposes the
myosin-binding sites.
Myosin binds actin,
and the muscle
contracts.
39. Skeletal systems
Endoskeleton: inside the animal
Exoskeleton: outside the animal
Hydrostatic skeleton: composed of
pressurized water in internal compartments.
49. Figure 6
Balance and locomotion
During walking and
running, the feet are
used for balancing,
pushing off, and
maintaining momentum.
50. Figure 7
Terrestrial locomotion
Stephen Dalton/Science Source.
Energy stored in tendons enables this frog to jump.
Editor's Notes
All muscle start as these spindly shaped cells from myoblasts – skeletal muscle cells fuse to form large fibers…
Satellite cells are small mononuclear progenitor cells with virtually no cytoplasm found in mature muscle. They are found sandwiched between the basement membrane and sarcolemma (cell membrane) of individual muscle fibres, and can be difficult to distinguish from the sub-sarcolemmal nuclei of the fibres. Satellite cells are able to differentiate and fuse to augment existing muscle fibres and to form new fibres. These cells represent the oldest known adult stem cell niche, and are involved in the normal growth of muscle, as well as regeneration following injury or disease.
It’s difficult to find the sartorius muscle in some people (cadavers)
Sarcomeres are multi-protein complexes composed of three different filament systems. The thick filament system is composed of myosin protein which is connected from the M-line to the Z-disc by titin. It also contains myosin-binding protein C which binds at one end to the thick filament and the other to actin.
The thin filaments are assembled by actin monomers bound to nebulin, which also involves tropomyosin (a dimer which coils itself around the F-actin core of the thin filament) and troponin.
Nebulin and titin give stability and structure to the sarcomere.
Z-line (from the German "Zwischenscheibe“). Each myofibril is made up of thin filament proteins and thick filament proteins, arranged (configured) in sarcomeres.
Each myofibril is made up of thin filament proteins, and thick filament proteins, arranged (configured) in sarcomeres
Titin is the largest known protein, consisting of 34,350 amino acids. Titin, also known as connectin is a protein that is important in the contraction of striated muscle tissues. Dystrophin, not Titin, is the protein absent in muscular dystrophy.
This interactive can be found as a separate file in your downloaded folder. This slide is a placeholder only. The image is a screen shot taken from the digital book.